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從Url讀取JSON java

2013-02-19 68 views
0

我在從一個URL獲取JSON時遇到問題。下面是代碼。從Url讀取JSON java

import java.io.BufferedReader; 
import java.io.FileNotFoundException; 
import java.io.FileReader; 
import java.io.IOException; 
import java.io.InputStreamReader; 
import java.net.URL; 
import java.util.List; 
import com.google.gson.Gson; 


public class Test_Application { 

    /** 
    * @param args 
    * @throws Exception 
    */ 
    public static void main(String[] args) throws Exception { 
     // TODO Auto-generated method stub 
     Gson gson = new Gson(); 

     String json = readUrl("http://api.wunderground.com/api/57dd9039b81a9c21/conditions/q/CA/San_Francisco.json"); 

     Page page = gson.fromJson(json, Page.class); 

     System.out.println(page.description); 
     System.out.println(page.language); 
     System.out.println(page.link); 
     System.out.println(page.title); 

    } 

    private static String readUrl(String urlString) throws Exception { 
     BufferedReader reader = null; 
     try { 
      URL url = new URL(urlString); 
      reader = new BufferedReader(new InputStreamReader(url.openStream())); 
      StringBuffer buffer = new StringBuffer(); 
      int read; 
      char[] chars = new char[1024]; 
      while ((read = reader.read(chars)) != -1) 
       buffer.append(chars, 0, read); 

      return buffer.toString(); 
     } finally { 
      if (reader != null) 
       reader.close(); 
     } 

    } 

    static class Page { 
     String title; 
     String link; 
     String description; 
     String language; 
     List<Item> items; 
    } 

    static class Item { 
     String title; 
     String link; 
     String description; 
    } 


}

輸出是：

null 
null 
null 
null

我認爲問題是，我有一個不恰當的類來讀取數據。這是正確的嗎？

感謝

編輯

網站返回如下：

{ 
    "response": { 
    "version": "0.1", 
    "termsofService": "http://www.wunderground.com/weather/api/d/terms.html", 
    "features": { 
     "conditions": 1 
    } 
    }, 
    "current_observation": { 
    "image": { 
     "url": "http://icons-ak.wxug.com/graphics/wu2/logo_130x80.png", 
     "title": "Weather Underground", 
     "link": "http://www.wunderground.com" 
    }, 
    "display_location": { 
     "full": "San Francisco, CA", 
     "city": "San Francisco", 
     "state": "CA", 
     "state_name": "California", 
     "country": "US", 
     "country_iso3166": "US", 
     "zip": "94101", 
     "latitude": "37.77500916", 
     "longitude": "-122.41825867", 
     "elevation": "47.00000000" 
    }, 
    "observation_location": { 
     "full": "SOMA - Near Van Ness, San Francisco, California", 
     "city": "SOMA - Near Van Ness, San Francisco", 
     "state": "California", 
     "country": "US", 
     "country_iso3166": "US", 
     "latitude": "37.773285", 
     "longitude": "-122.417725", 
     "elevation": "49 ft" 
    }, 
    "estimated": { 

    }, 
    "station_id": "KCASANFR58", 
    "observation_time": "Last Updated on February 19, 7:08 AM PST", 
    "observation_time_rfc822": "Tue, 19 Feb 2013 07:08:18 -0800", 
    "observation_epoch": "1361286498", 
    "local_time_rfc822": "Tue, 19 Feb 2013 07:08:31 -0800", 
    "local_epoch": "1361286511", 
    "local_tz_short": "PST", 
    "local_tz_long": "America/Los_Angeles", 
    "local_tz_offset": "-0800", 
    "weather": "Mostly Cloudy", 
    "temperature_string": "47.9 F (8.8 C)", 
    "temp_f": 47.9, 
    "temp_c": 8.8, 
    "relative_humidity": "87%", 
    "wind_string": "From the SW at 4.0 MPH Gusting to 13.0 MPH", 
    "wind_dir": "SW", 
    "wind_degrees": 225, 
    "wind_mph": 4.0, 
    "wind_gust_mph": "13.0", 
    "wind_kph": 6.4, 
    "wind_gust_kph": "20.9", 
    "pressure_mb": "1012", 
    "pressure_in": "29.90", 
    "pressure_trend": "-", 
    "dewpoint_string": "44 F (7 C)", 
    "dewpoint_f": 44, 
    "dewpoint_c": 7, 
    "heat_index_string": "NA", 
    "heat_index_f": "NA", 
    "heat_index_c": "NA", 
    "windchill_string": "46 F (8 C)", 
    "windchill_f": "46", 
    "windchill_c": "8", 
    "feelslike_string": "46 F (8 C)", 
    "feelslike_f": "46", 
    "feelslike_c": "8", 
    "visibility_mi": "10.0", 
    "visibility_km": "16.1", 
    "solarradiation": "", 
    "UV": "0", 
    "precip_1hr_string": "0.00 in (0 mm)", 
    "precip_1hr_in": "0.00", 
    "precip_1hr_metric": " 0", 
    "precip_today_string": "0.02 in (1 mm)", 
    "precip_today_in": "0.02", 
    "precip_today_metric": "1", 
    "icon": "mostlycloudy", 
    "icon_url": "http://icons-ak.wxug.com/i/c/k/mostlycloudy.gif", 
    "forecast_url": "http://www.wunderground.com/US/CA/San_Francisco.html", 
    "history_url": "http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=KCASANFR58", 
    "ob_url": "http://www.wunderground.com/cgi-bin/findweather/getForecast?query=37.773285,-122.417725" 
    } 
}

更新代碼

import java.io.BufferedReader; 
import java.io.FileNotFoundException; 
import java.io.FileReader; 
import java.io.IOException; 
import java.io.InputStreamReader; 
import java.net.URL; 
import java.util.List; 
import com.google.gson.Gson; 


public class Test_Application { 

    /** 
    * @param args 
    * @throws Exception 
    */ 
    public static void main(String[] args) throws Exception { 
     // TODO Auto-generated method stub 
     Gson gson = new Gson(); 

     String json = readUrl("http://api.wunderground.com/api/57dd9039b81a9c21/conditions/q/CA/San_Francisco.json"); 

     // Page page = gson.fromJson(json, Page.class); 
     Response response = gson.fromJson(json, Response.class); 

     System.out.println(response.termsOfService); 
     System.out.println(response.version); 

    } 

    private static String readUrl(String urlString) throws Exception { 
     BufferedReader reader = null; 
     try { 
      URL url = new URL(urlString); 
      reader = new BufferedReader(new InputStreamReader(url.openStream())); 
      StringBuffer buffer = new StringBuffer(); 
      int read; 
      char[] chars = new char[1024]; 
      while ((read = reader.read(chars)) != -1) 
       buffer.append(chars, 0, read); 

      return buffer.toString(); 
     } finally { 
      if (reader != null) 
       reader.close(); 
     } 

    } 

    static class Response{ 
     String version; 
     String termsOfService; 
    } 


}

來源

2013-02-19 Jeel Shah

+1

@downvoter，請問我有理由改善這篇文章？ – 2013-02-19 15:28:50

+0

網站返回什麼？ – 2013-02-19 15:29:15

+0

P.S.我沒有倒下。 – 2013-02-19 15:29:31

回答

2

替代GSON存在：

這個片段可以幫助做通用解碼器：

Map< String, Object > decoded = 
    gson.fromJson(data, new TypeToken< Map< String, Object>>() {}.getType());

下面的代碼是一個特定解碼器的開始：

import java.io.BufferedReader; 
import java.io.InputStreamReader; 
import java.net.URL; 

import com.google.gson.Gson; 

public class Test_Application 
{ 
    public static void main(
     String[] args) throws Exception 
    { 
     Gson gson = new Gson(); 
     String json = readUrl(
     "http://api.wunderground.com/api/57dd9039b81a9c21/" + 
     "conditions/q/CA/San_Francisco.json"); 
     System.out.println(json); 

     Map< String, Object > decoded = 
     gson.fromJson(
      json, 
      new TypeToken< Map< String, Object>>() {}.getType()); 
     System.out.println(decoded); 

     Answer answer = gson.fromJson(json, Answer.class); 
     System.out.println(answer.response.version); 
     System.out.println(answer.response.termsofService); 
     System.out.println(answer.response.features.get("conditions")); 
     System.out.println(answer.current_observation.image); 
     System.out.println(answer.current_observation.display_location); 
    } 

    static class Response 
    { 
     String    version; 
     URL     termsofService; 
     Map< String, String > features; 
    } 

    static class Observation 
    { 
     Map< String, String > image; 
     Map< String, String > display_location; 
     // TODO: complete me 
    } 

    static class Location 
    { 
     // TODO: complete me 
    } 

    static class Answer 
    { 
     Response response; 
     Observation current_observation; 
     Location display_location; 
     // TODO: complete me 
    }

在這種發展狀態它返回：

{response={version=0.1, termsofService=http://www.wunderground.com/weather/api/d/terms.html, features={conditions=1.0}}, current_observation={image={url=http://icons-ak.wxug.com/graphics/wu2/logo_130x80.png, title=Weather Underground, link=http://www.wunderground.com}, display_location={full=San Francisco, CA, city=San Francisco, state=CA, state_name=California, country=US, country_iso3166=US, zip=94101, latitude=37.77500916, longitude=-122.41825867, elevation=47.00000000}, observation_location={full=SOMA - Near Van Ness, San Francisco, California, city=SOMA - Near Van Ness, San Francisco, state=California, country=US, country_iso3166=US, latitude=37.773285, longitude=-122.417725, elevation=49 ft}, estimated={}, station_id=KCASANFR58, observation_time=Last Updated on February 19, 8:16 AM PST, observation_time_rfc822=Tue, 19 Feb 2013 08:16:18 -0800, observation_epoch=1361290578, local_time_rfc822=Tue, 19 Feb 2013 08:16:18 -0800, local_epoch=1361290578, local_tz_short=PST, local_tz_long=America/Los_Angeles, local_tz_offset=-0800, weather=Mostly Cloudy, temperature_string=48.7 F (9.3 C), temp_f=48.7, temp_c=9.3, relative_humidity=83%, wind_string=From the ESE at 1.0 MPH, wind_dir=ESE, wind_degrees=109.0, wind_mph=1.0, wind_gust_mph=0.0, wind_kph=1.6, wind_gust_kph=0.0, pressure_mb=1012, pressure_in=29.88, pressure_trend=-, dewpoint_string=44 F (7 C), dewpoint_f=44.0, dewpoint_c=7.0, heat_index_string=NA, heat_index_f=NA, heat_index_c=NA, windchill_string=49 F (9 C), windchill_f=49, windchill_c=9, feelslike_string=49 F (9 C), feelslike_f=49, feelslike_c=9, visibility_mi=10.0, visibility_km=16.1, solarradiation=, UV=0, precip_1hr_string=0.00 in (0 mm), precip_1hr_in=0.00, precip_1hr_metric= 0, precip_today_string=0.02 in (1 mm), precip_today_in=0.02, precip_today_metric=1, icon=mostlycloudy, icon_url=http://icons-ak.wxug.com/i/c/k/mostlycloudy.gif, forecast_url=http://www.wunderground.com/US/CA/San_Francisco.html, history_url=http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=KCASANFR58, ob_url=http://www.wunderground.com/cgi-bin/findweather/getForecast?query=37.773285,-122.417725}} 

0.1 
http://www.wunderground.com/weather/api/d/terms.html 
1 
{url=http://icons-ak.wxug.com/graphics/wu2/logo_130x80.png, title=Weather Underground, link=http://www.wunderground.com} 
{full=San Francisco, CA, city=San Francisco, state=CA, state_name=California, country=US, country_iso3166=US, zip=94101, latitude=37.77500916, longitude=-122.41825867, elevation=47.00000000}

來源

2013-02-19 15:47:40 Aubin

+0

一旦我填寫你指定的類，我應該能夠訪問數據的權利？ – 2013-02-19 15:57:17

+1

就像一個FYI（我只從其他WU JSON問題中知道）'Response'中的'features'實際上可以包含一堆東西，這就是爲什麼在我的Response中它是一個Map。我不知道可能性的完整列表;如果API文檔中包含所有這些對象的列表，您還可以創建一個完整的'Features'對象。 – 2013-02-19 15:58:42

+0

是的，但這很痛苦，如果您只想使用字段，帶有自定義分析器的通用Map 可能會有用。 – Aubin 2013-02-19 15:59:37

1

你的問題是，你的POJO與你的JSON不匹配。

JSON表示一個對象，並且您的POJO需要匹配它。這裏是什麼看起來像一個開始（沒有getter/setter方法公開所有領域只是爲了讓這個例子小）：

class MyWUPojo { 
    public Response response; 
    // more after this that match the JSON 
} 

class Response { 
    public String version; 
    public String termsofservice; 
    public Map<String, Integer> features; 
}

注意，一個需要注意的是，如果你只對部分感興趣的 JSON響應，這就是你必須實現的。 Gson會默默地忽略你沒有包含在你的POJO中的JSON的任何部分。

來源

2013-02-19 15:47:28

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